Moss on Roofs

Some of you may recall a comment I made in another thread about getting on to my insurance company about displaced tiles and a leaking roof.

My initial call to them resulted in them confirming that we had had some very severe winds in this area in the last month, and they notified their agent.

He has now been and says that there have been no high winds recently, and that the tiles have been forced off by moss, and the claim would be refused.

My local roofer, who I need to get the work done anyway, was surprised when I asked them to get rid of the moss, since they always believe that it helps to seal, and to bind in some cases, which I must say was always my view too.

"My local roofer, who I need to get the work done anyway, was surprised when I asked them to get rid of the moss, since they always believe that it helps to seal, and to bind in some cases, which I must say was always my view too."

Get a new roofer. A moss-covered roof is a ticking time bomb.

Far from having any beneficial effect, moss will ultimately lead to damaged and/or missing tiles.
Moss is most commonly found on sand-faced tiles, or old, handmade 'Tudor' type tiles that have a slightly rough surface. The tiny irregularities on these tiles provide the moss with a perfect substrate on which to grow.

Once moss is established on a roof it will hold water and atmospheric detritus, and in cold weather this will freeze. Repeated freezing and thawing cycles will lead to the breakdown of the tile surface (called spalling) and ultimately the failure of the tile - it will crack and leak, or part of it will fall away completely.

There are various compounds that can be applied to a roof to kill moss, but you'll have to repeat the exercise at frequent intervals. A common way to treat moss on a roof is to spray it with a copper sulphate solution. A better,longer lasting, but more drastic and expensive solution is to remove the ridge tiles and re-bed them with a thin strip of copper ribbon bedded along the bottom edges, projecting about 20mm from the tile edge. Rainwater will wash across the projecting strip and over time will treat the whole roof automatically.

if you go for the spray method make sure your roofer comes back after a while to clear all the dead moss that will accumulate in your gutters.

Whatever you decide to do, get rid of the moss completely, and don't let anyone tell you it is in any way good for a roof.

I was power washing my gutters before I left the UK and thought that I had foolishly began to get rid of moss at the same time on the roof tiles near the gutters. The washer took the moss of easily but also cleaned the tile and made them stand out. Didn't have time to do the whole roof so until it snows I have some old looking tiles and some new looking ones. I can't say her indoors was too impressed.

I guess I have a job to do when I return but it is reassuring to learn that it wasn't such a crazy idea after all.

I assume that these bad types of tile are no longer used by the building industry. Or would that be too simple a solution for the future. My house (bungalow) is about 40 years old and has moss on the roof which I clear away at intervals. Yes at 82 I still climb up there now and again to get shut of it.

But I think maybe I had better hand that job over to a younger person in future. Maybe my lady friend will be suitable as she is only 78. But I won't let her up there in frosty weather etc. as she might catch a cold.

I assume that these bad types of tile are no longer used by the building industry.

They are, but tile choices aren't always up to the builders. Planners have a say in a lot of cases, and if a property is in a conservation area there may be little choice. Then there are cases where an existing roof is patched, or partly replaced, and tiles must be matched.

Moss growth is influenced by other factors, too. Moss doesn't have roots - it needs a supply of flowing or standing water in order to grow and reproduce. That means you are less likely to get moss growth on a roof that has plenty of sun, or one that is subject to a lot of drying wind. Ideal conditions for moss are a shady, moist roof with lots of little irregularities in the tile surface. If a roof is overhung with tree branches that drip water onto the roof and prevent plenty of air movement there will eventually be moss growth to some degree.

In a spell of hot, dry weather when you look at a roof and think 'Good, the moss is all brown and dry, that's the end of it' don't be fooled - a few days rain and it will be green and healthy once more. Mosses are incredibly successful organisms, once they have established themselves.

Moss and any kind of growth are the worst things for Houses or any kind of Brick Concrete Building as they Eat the Building away. Bleach and Stiff Broom is a good way to clear it, but if they are concrete Tiles they will have become brittle and may break if trodden upon

"Moss and any kind of growth are the worst things for Houses or any kind of Brick Concrete Building as they Eat the Building away."

Mosses don't eat anything away. What happens, as I explained earlier in the thread, is that the moss grows in tiny crevices and irregularities on the substrate surface. Once established, mosses harbour accretions of air-borne and water-borne debris - tiny particles that form a soil-like compaction. The water that is held in the mosses and the debris freezes and thaws repeatedly over the years, and this action eventually breaks up the substrate surface. Frost will do this on its own, given time. Everyone has seen buildings with spalled bricks on the walls. This commonly happens to soft red bricks - the kind that were used in Tudor buildings, and on arches over the windows of more modern ones. Soft reds are sometimes called 'red rubbers' because they are easily shaped to make arches by rubbing them on a cutting sieve.

Concrete tiles are brittle from the moment they are manufactured. They are designed to be weight-bearing to a degree, but any roof tile will crack if you step on it in the wrong way.

Quote "grows in tiny crevices and irregularities on the substrate surface."
That's what I was talking about motor falls out as a result and other stuff crumbles, they also carry a lot of damp, that is no good to building when its held in place

My house must be different, it was built fifty-three years ago and has concrete tiles on a steeply pitched roof.

No real problem with moss although the valleys have been cleared once or twice and a drain pipe had to be cleared on one occasion. Moss sometimes becomes detached from the roof and bounces down in a lump.
My guttering and down pipes are vitreous enamel - do not know if this makes a difference but I imagine that the roof pitch helps.